1. Field
Example embodiments relate to an apparatus and method of processing a substrate. More particularly, example embodiments related to an apparatus for polishing a wafer and to a method of determining an end point of a polishing process by the same.
2. Description of the Related Art
An electronic system may include an integrated circuit chip on a printed circuit board, e.g., a controller such as a microprocessor, a memory chip such as a DRAM or flash memory, and so forth. To facilitate mass production, an integrated circuit chip may be formed on a semiconductor wafer.
Conventional formation of an integrated circuit chip on a semiconductor wafer may include selectively removing a portion of the semiconductor wafer, e.g., etching, polishing, and so forth. For example, conventional etching may include positioning the semiconductor wafer between bottom and top electrodes, followed by application of radio frequency (RF) voltage to the top/bottom electrodes to generate plasma for etching a portion of the semiconductor wafer or an object placed on the semiconductor wafer. In another example, conventional polishing may include a sponge roller contacting a semiconductor wafer, e.g., a beveled part or an edge part of the semiconductor wafer, and a solution supplied, e.g., via a nozzle, onto the semiconductor wafer.
Selective removal of portions of a semiconductor wafer may be followed by cleaning. For example, conventional etching, e.g., a reactive ion etching (RIE), may cause surface roughness on the semiconductor wafer, e.g., protrusions on edges of the semiconductor wafer. That is, by-products generated during the RIE may adhere to the semiconductor wafer, e.g., to an edge of the semiconductor wafer, so acicular protrusions may be formed thereon. Such protrusions may function as etch masks, e.g., interfering with proper etching, or may break to trigger generation of particles and impurities on the semiconductor wafer, thereby reducing production yield. Such protrusions may be removed by the cleaning process, e.g., secondary dry etching and/or polishing, before further processing, e.g., a photolithography process.
A conventional dry etching, however, may have an insufficiently precise detection of start/end points of the etching. For example, a conventional detection of start/end points of an etching process may include using an emission spectroscopy analysis, so an end point of the etching process may be determined according to concentration of an activated species easily observable, e.g., energy, ions, and so forth. For example, when an etching gas is used in the etching process, emission spectroscopy analysis may be used to measure concentration of a decomposed material or of reaction formation material of an etching gas in order to determine an end point of the etching process. The concentration may be determined according to variation in emission intensity based on a predetermined wavelength. For example, when using a CF gas, e.g., CF4 gas, to etch a silicon oxide layer, a wavelength of about 483.5 nm may be used to detect emission of a reaction product CO* during etching, so an etching end point may be determined by variation of emission intensity of the CO*. Similarly, when using a CF gas, e.g., CF4 gas, to etch a silicon nitride layer, a wavelength of about 674 nm may be used to detect emission of a reaction product N* during etching, so an etching end point may be determined by variation of emission intensity of the N*. Detection of an end point of an etching process via an emission spectroscopy analysis, however, may be difficult to conduct in real time without over-etching, thereby causing damage to underlying layers.
Another conventional detection of start/end points of an etching process may include using an end point detector (EPD) employing an emission spectroscope with a refraction lattice drivable by a motor. For example, when light generated in a plasma chamber is incident on the refraction lattice, e.g., through an optical fiber, the refraction lattice may divide the received light according to wavelengths to facilitate detection of a wavelength related to the undergoing process for measuring intensity thereof. Use of the EPD, however, may have several shortcomings.
First, in order to determine the wavelength related to the undergoing process, the EPD may require adjustment of a light reception angle of the refraction lattice and detection of light in the spectrum of about 200 nm to about 800 nm, so driving the refraction lattice may require a long time. Second, when intensity of a single wavelength over time is used to determine an end point of an etching process, it may be difficult to determine an end point of etching in small areas due to noise. For example, if a semiconductor wafer is mostly covered with a photoresist layer and only a very small portion thereof to be etched includes, e.g., silicon oxide, wavelengths corresponding to by-products due to the photoresist may be measured as a noise signal. As such, when an area of, e.g., silicon oxide, is small, e.g., about 0.5% of the semiconductor wafer or smaller, most measure signals corresponding to the silicon oxide may be buried in noise, and thus, may have a difficulty to be detected. Third, a change of light intensity may occur in response to causes other than type of an etched layer, e.g., a change in plasma density or a muddy EPD window, thereby causing inaccurate detection. Even if an additional wavelength is used to improve detection sensitivity of the EPD, a real time analysis may be difficult since the wavelength must be changed in the measurement of the existing single refraction lattice method.
A conventional polishing process may include polishing using a polishing tape. The conventional polishing tape may contact the semiconductor wafer during rotation thereof to remove surface roughness from the semiconductor wafer, and may continue polishing the wafer until an end point of the polishing is determined with respect to thickness of the wafer or with respect to a change in tension of the polishing tape contacting the semiconductor wafer. The conventional methods of determining an end point of the polishing, however, may not be sufficiently precise and/or efficient in real time.